In a data transmission system configured by connecting a plurality of apparatuses to one another in a cascade configuration (cascade connection) or in a data transmission system configured by connecting a plurality of apparatuses to one another in a ring configuration, it is necessary to set an apparatus number to each apparatus in order to transmit data among the plural apparatuses.
For example, in a known data transmission system 100 illustrated in FIG. 11, a plurality of slave apparatuses (denoted as “Slaves” 0 to 2 in the drawing) are connected in a cascade under the highest-ranked apparatus (denoted as “Master” in the drawing) functioning as a master apparatus.
In such data transmission system 100, each of the slave apparatuses 102 to 104 has to set its own apparatus number (address number) in the data transmission system 100.
By setting its own apparatus number in each of the slave apparatuses 102 to 104, each of the slave apparatuses 102 to 104 can confirm whether data transmitted from the master apparatus 101 is destined for itself or not, and can transfer data destined for another apparatus to the following slave apparatus 103 or 104.
There have been proposed techniques for automatically setting an apparatus number to each of a plurality of apparatuses in a data transmission system (refer to patent documents 1 to 4 below, for example).
As illustrated in FIG. 12, some techniques need an exclusive circuit 105 to 107 (denoted as “apparatus number automatically setting circuit” in the drawing) for automatically setting an apparatus number of its own slave apparatus 102, 103 or 104, for example.
[Patent Document 1] Japanese Patent Application Laid-Open Publication Number S62-271596
[Patent Document 2] Japanese Patent Application Laid-Open Publication Number H02-058944
[Patent Document 3] Japanese Patent Application Laid-Open Publication Number H05-344137
[Patent Document 4] Japanese Patent Application Laid-Open Publication Number H05-145562
According to the known techniques disclosed in the above patent documents, each of the slave apparatuses 102 to 104 has to always set its own apparatus number at the time of initial setting before data transmission, regardless of whether or not to require the exclusive circuit 105, 106 or 107 for automatically setting the apparatus number.
However, automatic setting of an apparatus number by each of the plural slave apparatuses 102 to 104 requires a considerable period of time, hence the larger the number of apparatuses configuring the data transmission system, the longer this period of time.